To get started, press Ctrl – Alt – T on your keyboard to open the terminal. When it opens, run the commands below to create a root password.
sudo passwd root
It will ask for your user password and then por de root password twice. With those steps you changed the root password for one you know
Next, run the commands below to enable root login in Ubuntu 12.10
sudo sh -c 'echo "greeter-show-manual-login=true" >> /etc/lightdm/lightdm.conf'
Restart your computer and select Login on the Login Screen. Then type the root username and password.